The flutes of, e.g., a twist drill, have two important functions, viz. on the one hand the forming of chips (including chipbreaking) and on the other hand the removal of these formed chips. The chip formation occurs in a space immediately behind each cutting edge, regardless of whether the edge is formed by a sharpening of the drill top as such, or by a separate cutting insert which is fastened on the tip, mechanically or, by, e.g., brazing. In this front space of a flute, the initially bandlike material that is separated off by the cutting edge from a workpiece, is forced to curl and break, thus creating separate chips with a particular form and size.
When designing drills of the abovementioned type there is often difficulty in achieving desired high cutting speeds since thermal cracks often appear at the active cutting corner where such thermal cracks usually appear.
It is a first object of the invention to accomplish a new type of drill that enables achieving higher cutting speeds during metal drilling.
It is a second object of the invention to accomplish a new type if drill wherein the inserts have such optimized formation that high cutting speed becomes possible without impairing the surface finish of the hole wall in the hole to be drilled.
It is a third object to provide a drill wherein the drill inserts have been given such optimized formation that increased cutting speed becomes possible during drilling while maintaining good lifetime of the drilling tool.
These and other objects are being achieved by means of a drill that has been given the characterizing features that are outlined in the appending claims.